1.3 Reacting Masses & Volumes Solution Chemistry IB Chemistry SL Mrs. Page 2015

Solutions Homogeneous mixture of two ore more pure substances Composed of a solute and a solvent Solute gets dissolved and is distributed evenly throughout the solvent (usually present in smaller amount) Solvent dissolves the solute (usually present in larger amount) When solvent is water the solution is known as an aqueous solution.

Types of Solutions Not all solutions involve a solid dissolved in a liquid. Examples of Solutions: Air - O2(g) dissolved in mostly N2(g) Soda water – CO2(g) dissolved in H2(l) Vinegar – acetic acid dissolved in water Sugar syrup – sugar dissolved in water Dental filling – Hg(l) dissolved in Ag(s) Brass – Zn(s) dissolved in Cu(s) Steel – C(s) dissolved in Fe(s)

Concentrations A solution is said to be saturated when a solvent cannot dissolve any more solute.

Concentrations Molar Concentration: the amount (mol) of a substance dissolved in 1 dm3 of solvent. 1 dm3 = 1 L 𝒄𝒐𝒏𝒄𝒆𝒏𝒕𝒓𝒂𝒕𝒊𝒐𝒏 (𝒄)= 𝒎𝒐𝒍 (𝒏) 𝑽 ( 𝒅𝒎 𝟑 ) Molarity = concentration in mol dm-3 Denoted using brackets [HCl]= 1.00 mol dm-3 Sometimes we express concentration as grams per volume (g dm-3) When dealing with very dilute concentrations we may use units of parts per million (ppm)

Concentrations Molar Concentration: the amount (mol) of a substance dissolved in 1 dm3 of solvent. 1 dm3 = 1 L 𝒄𝒐𝒏𝒄𝒆𝒏𝒕𝒓𝒂𝒕𝒊𝒐𝒏 (𝒄)= 𝒎𝒐𝒍 (𝒏) 𝑽 ( 𝒅𝒎 𝟑 ) Molarity = concentration in mol dm-3 Denoted using brackets [HCl]= 1.00 mol dm-3 When dealing with very dilute concentrations we may use units of parts per million (ppm)

Concentrations Problems A solution of sodium hydroxide has a concentration of 8.00 g dm-3. what is the concentration in mol dm-3? 8.00 𝑔 𝑑𝑚 3 × 1 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 39.91 𝑔 = 0.200 mol dm-3 Calculate the concentration of a 0.0400 mol dm-3 solution of sodium carbonate (Na2CO3) in g dm-3 0.0400 𝑚𝑜𝑙 𝑑𝑚 3 × 105.99𝑔 1 𝑚𝑜𝑙 = 4.24 g dm-3

Standard Solutions 500. 𝑐𝑚 3 ∙ 1 𝑑𝑚 3 1000 𝑐𝑚 3 =0.500 𝑑𝑚 3 A solution of known concentration Calculate the mass of copper (II) sulfate pentahydrate, CuSO4●5H2O required to prepare 500.cm3 of a 0.400 mol dm-3 solution. 500. 𝑐𝑚 3 ∙ 1 𝑑𝑚 3 1000 𝑐𝑚 3 =0.500 𝑑𝑚 3 0.400 𝑚𝑜𝑙 𝑑𝑚 3 ∙ 249.72 𝑔 𝑚𝑜𝑙 ∙0.5 𝑑𝑚 3 = 49.9 g CuSO4●5H2O

Titrations We use standard solutions to find the concentration of unknown solutions Volumetric Analysis: analyzing the composition of a solution by using the volume of a standard solution need to react with the volume of an unknown solution Titration: a technique for using volumetric analysis (often with acid-base reactions) Equivalence point when the reaction is completed

Titrations When using acid-base reactions you can use an indicator to show when the reaction has come to completion Phenolphthalein – colorless in acid, pink in base Methyl Orange – pink in acid, orange neutral, yellow basic For next Class: Watch and Write Procedure & Make Data Table https://www.youtube.com/watch?v=HwKFcjGHN_4

Titrations What volume of HCl with a concentration of 2.00 mol dm-3 would have to be added to 25.0 cm3 of a 0.500 mol dm-3 sodium carbonate solution to produce a neutral solution of sodium chloride? Na2CO3(aq) + 2HCl(aq)  2NaCl(aq) + H2O(l) + CO2(g) 0.025 𝑑𝑚 3 ∙ 0.500 𝑚𝑜𝑙 𝑁𝑎 2 𝐶𝑂 3 𝑑𝑚 3 ∙ 2 𝑚𝑜𝑙 𝐻𝐶𝑙 1 𝑚𝑜𝑙 𝑁𝑎 2 𝐶𝑂 3 ∙ 𝑑𝑚 3 2.00 𝑚𝑜𝑙 = 0.0125 𝑑𝑚 3 ∙ 1000 𝑐𝑚 3 1 𝑑𝑚 3 =12.5 𝑐𝑚 3

Titrations 25.00 cm3 of 0.100 moldm-3 sodium hydrogencarbonate solution was titrated with dilute sulfuric acid. 15.2 cm3 of acid was needed to neutralize the solution. 2NaHCO3(aq)+ H2SO4(aq)  Na2SO4(aq) + 2H2O(l) + 2CO2(g) Calculate the concentration of the sulfuric acid Calculate the volume of carbon dioxide, measured at STP produced during the titration.

Titrations Calculate the mass in g of H2SO4 required to prepare 500 cm3 of a 2.0 mol dm-3 solution of sulfuric acid. A solution of aluminum bromide, AlBr3 is to be used in the laboratory during an electrolyte investigation. Calculate the total number of ions present in 2.5 dm3 of a 1.6 mol dm-3 solution of AlBr3. Calculate the volume, in dm3, of 0.390 mol dm-3 potassium hydroxide, KOH solution that will neutralize 25.0 cm3 of 0.350 mol dm-3 sulfuric acid H2SO4.